The prior art in the field of disposable absorbent articles for topical application to the skin of a wearer is particularly developed in the field of band-aids, plasters and bandages. These articles are often breathable, but typically applied in an emergency situation where for example a cut into the skin of the wearer has occurred and absorption of the body liquids emanating from a wound is desired. In this context performance aspects of the absorbent article such as comfortable and easy use and application, painless removal, discreteness are subordinate to criteria such as sterility, healing support, mechanical protection of the wound. Also such wound covering absorbent articles are mostly used in skin areas where prior to application of the absorbent article body hair can be removed or where little or no hair grows.
The present invention does not relate to wound covering absorbent articles but relates to breathable absorbent articles for absorption of body liquids which naturally emanate from a body without a wound. For example breathable sanitary napkins or pantiliners for use in the genital region are such articles. Also breathable incontinence devices which are worn e.g. in the genital region or breathable sweat pads which are worn in the arm pit region of a person are the subject of the present invention.
If such articles are applied to the skin of a wearer in a region were typically a considerable amount of hair grows then the criteria of easy and painless removal of the article is of key importance. Such articles have generally been disclosed in US statutory invention registration H1602 or WO 96/33683. Some more details of such articles have been considered for example in PCT application WO 95/16424. In this document sanitary articles having a body adhesive which is applied on the wearer facing side of a sanitary napkin along the entire periphery are disclosed. The problem underlying this document is primarily the safe attachment to the skin but mentions also the problems of detachment of such articles after use without causing undue pain to a wearer.
The disclosure of WO 95/16424 includes a detailed analysis of the criteria for the body adhesive in respect to rheological criteria. However, this document has little regard to the problem of painless removal of such articles since the rheological criteria taught include epilatory, i.e. hair removal, compositions which are commercially available such as STREP MIELE.TM. sold in Italy by Laboratori Vaj S.p.A. The adhesives for topical attachment mentioned in WO 95/16424 include also today's pressure sensitive adhesives which are used to attach sanitary napkins to undergarments. Further, this document only identifies static rheological characteristics but is silent as to the dynamic rheological behaviour of a body adhesive.
In WO 96/13238 a frequency dependent body adhesive model is disclosed. However, all measurements disclosed, e.g. on page 9, were made at temperatures between -60.degree. C. and +120.degree. C. and at actual frequencies of 0.1 to 100 rad/s. In order to obtain the necessary data at application temperature (about 20.degree. C., typical bath room, i.e. storage temperature) the Williams-Landel-Ferry (hereinafter WLF) equation was used.
This WLF equation is empirical and only valid within certain limits e.g. it cannot be used to extrapolate to temperatures below the glass transition temperature of a polymeric adhesive also the WLF cannot be used on the basis of values obtained below the glass transition temperature. Details about the WLF equation and its applicability can be found in "Principles of Polymer processing" by Z. Tadmor and C. G. Gogos, published by John Wiley & Sons or in "Viscoelastic Properties of Polymers" by J. D. Ferry also published by John Wiley & Son. Since this is already missing from WO 96/13238 the applicability of the disclosed data cannot be assessed. Further this disclosure does not relate to self adhesive articles which are breathable.
European Patent Application EP-638 303 discloses the use of a body adhesive on side cuffs of sanitary napkins in order to keep the cuffs in an upright position. Swiss publication CH-643730 discloses the use of a very long sanitary napkin having chamfered outer edges with a body adhesive at the four corners of the outer edges in order to provide a body adhesive area well outside the region of public hair growth.
Further improvements in the definition and formulation of body adhesive now allow an improved direct attachment of absorbent articles to the skin. However, such close wearing conditions also cause a problem since the absorbent articles have an impermeable plastic film on their outer surface. This causes sweating and a temperature raise inside the article, usually described as stuffiness, which is unacceptable at least to sensitive users of such articles. This problem is substantially more pertinent for articles attached to the skin of a wearer than for articles attached to a garment because these articles allow breathability through their wearer facing surface.
Based on the above state of the art it is an objective of the present invention to provide disposable absorbent articles for absorption of natural emanating liquids from the body of a wearer which are attached to the skin of a wearer, allow painless removal of the absorbent article and do not suffer from stuffiness. It is another objective of the present invention to ensure upon removal of the absorbent article that no residual adhesive remains on the skin or on the hair of the wearer. It is yet another objective of the present invention to provide disposable absorbent articles which are worn in such close proximity to the liquid emanating area of the wearer that liquid losses to the outside of the absorbent article is minimised or eliminated, without stuffiness resulting from the close proximity. For disposable absorbent articles worn in the crotch region of a wearer this will translate into an improved security against soiling of the surrounding skin tissue and clothing.
In addition to the above objectives of the present invention it is also desirable for sanitary napkins, pantiliners and catamenial devices to reduce or even eliminate odour emanating from the product since its application to the skin of the wearer provides an odour seal which prevents odours of the absorbed liquid or forming from the absorbed liquid to reach beyond the absorbent article.